The present invention relates to a spark plug having an electrode connected to an ignition lead via a terminal stud and having a resistor arranged between the electrode and the ignition lead.
Spark plugs are known that use high-voltage to effect an arcing between the ground electrode and the center electrode of the spark plug in the combustion chamber of an internal combustion engine and thus ignite an air-fuel mixture that is compressed in the combustion chamber of the internal combustion engine. It is also known, in these spark plugs, to provide a resistor arranged between the ignition lead and the center electrode.
The resistor, which is arranged between the ignition lead and center electrode inside the spark plug, raises the total electrical resistance of an arrangement composed of ignition lead and spark plug. As a result of this increase in resistance, the electrical current flow within the ignition lead and the spark plug is smaller, as a result of which the level of the ignition voltage is stabilized, i.e., the voltage source producing the ignition voltage experiences smaller loads due to increased resistance in the ignition lead and spark plug, thus making it possible to maintain the ignition voltage level at a virtually constant value. The level of high voltage made available by the voltage source is of decisive importance for spark plugs, in permitting the ignition spark to form in the first place.
The level of the ignition voltage required by the spark plug in order to generate a spark between the electrodes is less than the voltage level supplied by the high voltage generator. This difference between the high-voltage supply and the actually required ignition voltage is designated as the voltage reserve. The voltage reserve is necessary to cover the increasing ignition voltage requirements due to the increasing distance between the electrodes during the course of the service life of the spark plug. Thus, if the difference between the high-voltage supply and the ignition voltage, i.e., the voltage reserve, is particularly high, then reliable ignition of the air-fuel mixture within the combustion chamber nevertheless results even if the distance between the two electrodes of the spark plug has become greater through the erosion of the electrodes, or if other parameters of the combustion process, for example, a too-thin air-fuel mixture, or deposits such as carbon black or carbonized oil, built up on the electrode from the combustion process, make necessary increased ignition voltage demand.
As a result of the decreased electrical current flow, due to increased resistance, the wear and tear on the electrodes from erosion also decreases. A smaller current flowxe2x80x94during the time that an electric arc burns between two electrodesxe2x80x94thus brings about a reduction in metal deposits on the electrodes. As a result of the smaller metal deposits, the service life of the spark plug is increased.
A further objective of the resistor between the ignition lead and the center electrode is the so-called xe2x80x9csuppression of interference.xe2x80x9d The suppression of interference is achieved in that the resistor in the lead to a spark gap of the spark plug limits the transmission of interference pulses to the ignition leads, and thus lessens the radiated interference.
One conventional resistor used is composed of a mixture of glass, iron, carbon black, and polymer particles. Resistors of this type, however, have but slight resistance to temperature. Therefore conventionally, the resistor in the spark plug is arranged in the cooler area, thus in the area furthest from the engine.
The present invention relates to a spark plug having an electrode, preferably the center electrode, that is connected to an ignition lead via a terminal stud, and having a resistor arranged between the electrode and the ignition lead, the resistor having increased resistance to temperature. This spark plug has the advantage that the resistor can be disposed in the front areas of the spark plug, thus in the vicinity of the center electrode, as a result of which, surprisingly, reduced electrode and insulation erosion takes place and, moreover, an improved xe2x80x9csuppression of interferencexe2x80x9d is assured.
The reduced electrode and insulator erosion significantly improves the service life of the spark plug. Similarly, as a result of the reduced electrode wear, the distance between the two electrodes of the spark plug, i.e., between the center electrode and the ground electrode, is maintained virtually constant over a longer time period. If the distance between the two electrodes is approximately constant, as mentioned above, the result is that the ignition voltage demand of the spark plug remains virtually constant, the difference between the high voltage supply and the ignition voltage thus remaining at a high level, in other words, improving the voltage reserve.
In manufacturing a temperature-resistant resistor, glass or glass ceramic materials, preferably powder, are used that are preferably metalized with zero current. These materials contain neither carbon black nor temperature-unstable polymers, so that an increased resistance to temperature is assured. The structure of the resistor, in this context, is composed of a metal phase configured as a network and a glass matrix surrounding the metal phase, or a glass ceramic matrix that preferably has a layer film thickness of a few nm. In one preferred embodiment, the metal phase is manufactured using metals or metal alloys of high temperature resistance such as nickel/tungsten, platinum, or platinum/palladium. Metals or metal alloys having a high resistance value may be used so as to enable the manufacturing of resistor layers which are only a few nm, particularly 0.5-6 nm, thick.
The processes for manufacturing conventional spark plugs can very easily be transferred in an advantageous manner to the spark plug according to the present invention having a temperature-resistant resistor.